In the past, there has been proposed an illuminating device suitable including a light source including light emitting diodes (LEDs) (e.g., see JP 2005-259653 A (hereinafter referred to as “Document 1”)). The illuminating device disclosed in Document 1 includes a casing with a box shape, a light source, a collimator lens part, and a fly eye lens, for example. The casing includes a top plate having a circular window hole, a pair of side plates protruding upright from opposite ends of the top plates, and a bottom plate which interconnects the pair of side plates and is positioned parallel to the top plate. The bottom plates has transmitting holes which have diameters smaller than a diameter of the window hole and are arranged in a matrix manner. The light source includes a circuit board with a rectangular plate shape, and bullet LEDs mounted on the circuit board. Tops of the bullet LEDs are inserted into the transmitting holes of the bottom plate, individually.
The illuminating device disclosed in Document 1 is configured to convert rays of light emitted from the light source into collimated rays of light by the collimator lens part and guide the collimated rays of light to the fly eye lens.
Recently, surface mounted LEDs and COB (Chip On Board) LEDs are the mainstream of LEDs for illumination. However, in a case where such surface mounted LEDs and COB LEDs are used as a light source, it may be difficult for the configuration disclosed in Document 1 to improve the usage efficiency of light emitted from LEDs and additionally improve the uniformity ratio of illumination light.